The heart rate for adults is typically time invariant for given levels of activity and excitement and a normal relaxed, resting heart rate is on the order of 60-80 beats per minute (bpm). However, babies are normally born with a very high intrinsic resting heart rate compared to adults. It can often start as high as 120 bpm. The pediatric heart rate then typically climbs to a peak of approximately 150 bpm at two weeks of age, holds at approximately that rate for about two months, and then tapers off as the child ages until the heart rate reaches its adult level. It should be understood that children, like adults, experience normal instantaneous variation in heart rate due to sleep/wake cycles, eating, physical exertion, and the like.
Implantable cardiac devices, such as pacemakers and implantable cardioverter defibrillators, are known devices that are implanted in patients experiencing heart arrhythmias. Pacemakers typically monitor the beating of the heart and provide artificial stimulation to the heart to override brady/tachycardia and other arrhythmias. Implantable cardiac devices typically are programmed with a basic pacing rate and are set to deliver a pacing pulse of at least the basic pacing rate if the heart does not do so itself. Generally, implantable pacemakers include sensors that detect the intrinsic heart activity. They also include sensors that detect parameters indicative of the patients level of activity and metabolic need. These sensors can include activity sensors, transthoracic impedance sensors and the like that send signals to the control unit of the implantable cardiac stimulation device to ensure that the heart rate is maintained at a level consistent with the patient's activity.
With many patients, the implantable pacemaker is a demand-type pacemaker that only provides a pacing pulse when it detects the absence of an intrinsic heart event. In this way, the pacing is kept to a minimum. Hence, pacemakers are typically programmed with a basic pacing rate that can be adjusted upwards based upon the observed activity level and metabolic need of the patient. The basic pacing rate is thus used as a benchmark to determine when to apply a pacing pulse to the patient based upon the observed intrinsic activity of the patient.
Progress in reducing the size of pacemakers and other implantable cardiac stimulation devices has made them a feasible option for pediatric patients. Pediatric patients can have arrhythmias with observable characteristics similar to those seen in adults. Hence, pacemakers have been implanted in pediatric patients in order to regulate heart function. These pediatric pacemakers can include features and circuitry that allow for the delivery of demand-type pacing pulses and also allow for the adjustment of the pacing rate depending upon the activity and the metabolic need of the pediatric patient in a similar manner as described above.
However, the aforementioned variation in the child's intrinsic heart rate over time typically requires repeated adjustment of the pacemaker's intrinsic pacing rate by a physician. As discussed above, the pediatric patient's intrinsic heart rate is varying very significantly during the first several months of life. If the basic pacing rate is not adjusted, the pediatric patient heart may beat at a rate that is either too high or too low which can cause discomfort or even impair the health and development of the pediatric patient.
It will be appreciated that repeated visits to or by a physician are an inconvenient and expensive proposition for the patient and its family. As discussed above, the intrinsic heart rate of the pediatric patient can be varying significantly on a day-to-day basis requiring multiple trips to the physician during the first several weeks of life. These trips can be quite stressful for both the patient and the parents of the patient.
From the foregoing, it will be appreciated that there is a need for a pacemaker that is suitable for use with pediatric patients that requires less follow up visits. To this end, there is a need for a pediatric pacemaker that requires less adjustment after implantation.